628
FXUS61 KBOX 160153
AFDBOX

Area Forecast Discussion
National Weather Service Boston/Norton MA
953 PM EDT Sun Sep 15 2024

.SYNOPSIS...
Strong area of high pressure over the northeast will continue
the dry and quiet weather through Tuesday. A broad low brings
our next shot of unsettled weather mid to perhaps late in the
week. Risk for showers greatest along the south coast. Turning
drier late in the week and heading into the weekend with near to
cooler than seasonable temperatures.

&&

.NEAR TERM /UNTIL 6 AM MONDAY MORNING/...
955 PM Update...

Going forecast still looks on track, and other than
incorporating current obs in the forecast, no significant
changes were needed. Temps have cooled off into the mid to upper
50s for southeast MA and portions of RI, and in the lower to mid
60s more common north and west of I-95. Still have several more
hrs of good radiational cooling ahead of us, and that could
support patchy fog development in the CT Valley and around the
I-495 corridor in eastern MA where radiational fog is more
favored to develop.

Previous discussion...

High pressure across SNE will provide clear skies and light to
calm winds setting the stage for excellent radiational cooling
conditions. Lows will drop into the 40s in the traditional
colder radiator locations, otherwise low-mid 50s. Current
dewpoints are higher than the forecast low temps so we expect
patchy radiation fog to develop, especially in the CT valley
and portions of eastern MA.

&&

.SHORT TERM /6 AM MONDAY MORNING THROUGH MONDAY NIGHT/...
Monday...

Center of high pres shifts east of New Eng but ridging extends west
across the region through Mon night. Expect lots of sunshine again
although high clouds will begin to overspread the region from the
south and west during the afternoon. Slight warming in the low
levels so it`ll be another warm day with highs possibly reaching low-
mid 80s in the CT Valley and interior NE MA, with mid-upper 70s
closer to the coast. The column is pretty dry with axis of lower
PWATs across SNE so mixing will result in dewpoints dropping into
the 40s and lower 50s.

Monday night...

High clouds well north of sub-tropical low pres will continue to
increase and thicken across SNE through the night. Also, increasing
shallow low level moisture will lead to development of stratus and
fog near the south coast. More cloud cover will lead to milder temps
with lows ranging through the 50s.

&&

.LONG TERM /TUESDAY THROUGH SUNDAY/...
Highlights

* Another dry and mild day Tue, but will have increasing cloudiness.

* Unsettled mid to perhaps late in the week with showers. Confidence
  highest along the immediate south coast. Northern periphery of
  precip shield still questionable at this point. Temps trending
  more seasonable.

* Turning drier this weekend

Tuesday...

A ridge still builds from New England into the Great Lakes region
early on Tue. The ridge axis shifts offshore toward Nova Scotia by
late Tue, while the cutoff over the TN/OH Valley slowly rotates
northward. High pressure nudges into southern New England from just
south of Nova Scotia on Tue.

Dry and quiet weather expected with high pressure still controlling
the weather. Will see increasing high clouds as the day progresses
ahead of the next system impacting our region. Can see this quite
clearly per the 500-300 hPa RH with deterministic guidance, but
think there will be breaks of sun, especially earlier in the day.
Mild once again with high temps ranging from the mid 70s to the mid
80s.

Tuesday Night through Friday...

Cutoff over the OH/TN Valley initially will gradually rotate
northeastward toward the Mid Atlantic. A shortwave lifts toward
southern New England on Wed on the eastern side of the cutoff before
lifting through/offshore by Thu. Still may have the cutoff south of
our region on Fri or absorbed into a trough, lot of uncertainty with
hows things evolve. A broad low lifts toward our region Tue Night
into Thu before shifting offshore.

This will be our next opportunity for showers across southern New
England. Main change I`ve made from the NBM is to slow down the
progression of PoPs as the NBM is much too fast/high in bringing
chances in based on the consensus of deterministic guidance Tue
Night through much of Wed. Really think that Wed PM through Thu NBM
much more dialed in as this coincides with the placement/timing of a
20-30+ kt 925 hPa E to NEly low level jet. This is also where we tap
into 1-2+ inch PWATs. At this point most confident in precip
amounts/chances for the immediate south coast, whereas think there
could be a tight N/S gradient with little if any precip along/north
of the MA Turnpike. Tried to highlight this with higher chances of
precip, but let NBM take over with lower chances further north given
there is still uncertainty on where the jet lines up and how far
north things track.

Other change made from the previous forecast was to remove the Day 4
ERO in collab with WPC. Antecedent conditions have been quite dry
leading into this event. So, would take a fair amount of rainfall
for flash flooding. Ensembles still in the two camps of EPS/GEPS
being much wetter than the GEFS. At this point 24 hr probs of AOA 1
inch in a 24 hr period are low to mod (10-50 percent) centered
mainly by the Thu timeframe, while the GEFS is still nil. Even with
the wetter end of guidance (GEPS) the interquartile range for our
area is anywhere from 0.25 to 2 inches of rain, which is much needed
at this point. Highest amounts still centered more toward the south
coast for this timeframe. High temperatures trending near to cooler
than seasonable through this timeframe with the prolonged easterly
flow.

Fair amount of uncertainty on Fri on if things clear out a bit
quicker with high pressure nudging in from the north. Due to the
uncertainty have just stuck with the NBM for now, which keeps slight
chances of precip.

Saturday...

Ridge axis builds from the Mississippi River Valley into the Great
Lakes region. Though there still are questions on where the upper
trough/cutoff in the prev period is located. High pressure nudges in
or is overhead during this period.

Turning drier during this timeframe with high pressure back in
control. Will definitely feel more like fall with high temps
generally in the 60s.

&&

.AVIATION /02Z MONDAY THROUGH FRIDAY/...
Forecast Confidence Levels:

Low - less than 30 percent.
Moderate - 30 to 60 percent.
High - greater than 60 percent.

Tonight and Monday...High confidence.

VFR, but patchy late night MVFR to IFR stratus and fog may
develop in the CT valley and portions of interior eastern MA.
E-SE wind 5-10 kt this afternoon, light to calm winds tonight,
then S-SE wind 5-10 kt Monday.

Monday night...Moderate confidence.

Areas of late night MVFR/IFR stratus and fog may develop near
the south coast overnight, otherwise VFR.

KBOS TAF...High confidence.

KBDL TAF...High confidence.

Patchy stratus/fog developing roughly 06-09Z until daybreak.
Any fog developing should clear out quickly.

Outlook /Tuesday through Friday/...

Tuesday: VFR.

Tuesday Night: VFR. Slight chance SHRA.

Wednesday through Thursday: VFR. Chance SHRA.

Thursday Night: VFR. Breezy. Chance SHRA.

Friday: Mainly VFR, with local IFR possible. Breezy. Slight
chance SHRA.

&&

.MARINE...
Forecaster Confidence Levels:

Low - less than 30 percent.
Medium - 30 to 60 percent.
High - greater than 60 percent.

Tonight through Monday night...High confidence.

High pres over the waters will result in favorable boating
conditions with winds below 20 kt, varying from E to S, and seas 3
ft or less. Areas of marine fog expected to develop over south
coastal waters Mon night leading to reduced vsbys.

Outlook /Tuesday through Friday/...

Tuesday: Winds less than 25 kt.

Tuesday Night: Winds less than 25 kt. Seas locally approaching
5 ft. Slight chance of rain showers.

Wednesday: Winds less than 25 kt. Seas locally approaching
5 ft. Chance of rain showers.

Wednesday Night: Winds less than 25 kt. Areas of seas
approaching 5 ft. Rain showers likely.

Thursday: Winds less than 25 kt. Areas of seas approaching
5 ft. Chance of rain showers.

Thursday Night: Winds less than 25 kt. Seas up to 5 ft. Chance
of rain showers.

Friday: Winds less than 25 kt. Areas of rough seas. Slight
chance of rain showers.

&&

.BOX WATCHES/WARNINGS/ADVISORIES...
CT...None.
MA...None.
RI...None.
MARINE...None.

&&

$$

SYNOPSIS...KJC/BL
NEAR TERM...KJC/Loconto/BL
SHORT TERM...KJC
LONG TERM...BL
AVIATION...KJC/Loconto/BL
MARINE...KJC/Loconto/BL